Here are 20 of the best SEO plugins to help you choose the right tags, tell search robots what to work on, optimize your post titles and more.

All in One SEO Pack – One of the most popular plugins ever for WordPress, this plugin does a bit of everything for you from helping choose the best post title and keywords, to helping you avoid duplicate content and more.

Automatic SEO Links – Automatic SEO Links allows you to choose a word or phrase for automatic linking, both internal and external, set anchor text, choose if it should be “nofollow” or not, and more. One of the best features of this plugin is that it will only do this for the first occurrence of a word in a post so you don’t have to worry about spamming your post with numerous links to the same thing.

Google XML Sitemaps – An essential tool in any blogger’s armory of SEO tools. While the name only mentions “Google,” this plugin creates an XML-sitemap that can be read by Ask, MSN and Yahoo also.

HeadSpace2 – This plugin allows you to install all sorts of meta-data, add specific JavaScript and CSS to pages, suggests tags for your posts and a whole lot more.

Meta Robots WordPress plugin – An easy solution for adding robot metadata to any page you choose on your blog. You can use it to make your front page links into “nofollows,” prevent indexing of search pages, disable author and date-based archives, prevent indexing of your login page and numerous other features.

Nofollow Case by Case – This plugin allows you to strip the “nofollow” command from your comments, and then you can apply it to only the comments you don’t wish to support.

Platinum SEO Plugin – The Platinum SEO Plugin offers you such features as automatic 301 redirects for permalink changes, auto-generation of META tags, post slug optimization, help in avoiding duplicate content and a host of other features.

Redirection – For any number of reasons you sometimes need to move a page from one spot on your blog to another, but then you risk losing that page’s status in search results. Redirection helps you with your 301 redirects, captures a log of 404s so you can work on correcting them, sets up an RSS feed for errors and more.

SEO Blogroll – Do you worry that the people you link to in your blogroll are feeding off of your PageRank? With SEO Blogroll you can make separate sections for various groupings of links, with an unlimited number in each, and all of them will receive the “nofollow” attribute.

SEO for Paged Comments – With the introduction of paged comments in WordPress 2.7, there was a potential problem with search engines thinking you had duplicate content as the post would appear on each page. This plugin aims to take care of this issue for you until the folks at WordPress change things up.

SEO friendly and HTML valid subheadings – Some themes for WordPress will confuse your sub-header tags based on the page they are to be displayed on, but this plugin will automatically reset them to make them more SEO friendly by moving them down one spot in the hierarchical tree. In other words, h2 becomes h3, h3 becomes h4 and so on.

SEO Friendly Images – Images can be a great source of traffic as people search for images of various subjects, and this plugin helps you with making sure that you have “alt” and “title” tags on all of your images so that the search engines can properly index them.

SEO No Duplicate WordPress Plugin – If you must have duplicate content on your site for whatever reason, SEO No Duplicate will allow you to state which version of the post search engines should index while ignoring the others.

SEO Post Link – The post slug is the blog title you see in a browser’s URL bar, and if it’s too long, search engines won’t take a liking to it. SEO Post Link comes with an already populated list of words to cut from a title when it turns into a URL to make your post addresses that much friendlier. You can set it so that it’s limited to a certain number of characters, cut short words, cut unnecessary words and more.

SEO Smart Links – Interlinking your blog can be the key to getting more people to read more of your posts, but it is time consuming and tedious to do it by hand. SEO Smart Links does this for you automatically when you tell it what words to link to what URLs, and it also allows you to set “nofollow” and “open in window” comands for the links.

SEO Tag Cloud Widget – Love ‘em or hate ‘em, a lot of people use tag clouds on their blogs. Since their inception they have been fairly unreadable by search engines, but with this plugin they will be converted to an SEO-friendly HTML markup that can be indexed.

SEO Title Tag – Your tags are an important part of your site for making sure that search engines know where to place your posts, and SEO Title Tag focuses exclusively on this. Unlike some other plugins, and WordPress itself, this extension will allow you to add tags to your pages, your main page and even any URL anywhere on your site.

Simple Tags – An extremely popular plugin that focuses on helping you choose the best tags for your posts by offering suggestions, auto-completion of tags as you type, an AJAX admin interface, mass tag editing and a whole lot more.

Sitemap Generator – This is a more customizable sitemap generator than most with options to support multi-level categories and pages, category/page exclusion, permalink support, choices on what to display, options to show number of comments and more.

TGFI.net SEO WordPress Plugin – This particular plugin will do most of the usual SEO work of optimizing titles and keywords, but it adds a unique twist as it is mainly directed at people who use WordPress as a CMS.

Rich media is easy. Well, it takes some work, and there is some learning involved, but plugin developers have made it much easier to adorn our sites with the glitz and glamor of all things interactive. Play with some of them and see what they’re capable of. You’ll be amazed at how far this medium can take your site and how you’ll be better able to serve your site visitors.

So what kinds of plugins are out there and what are they capable of? Let’s find out, shall we?

All-In-One Video Pack

This is a fully-functioning video tool. You an import, upload, and record video right in the post. Video editing, mixing, thumbnails, video players, and other features that rival those found on YouTube can be added as well.

The whole thing installs pretty easily and sets up pretty quick. If you’re going to get the most of this plugin, however, take some time to explore everything, read up on the features, and play with it. This is a fantastic option for those looking to try vlogging, artists, and those who currently use a number of different social networks for their videos.

WPaudio MP3 Player

If you’re a podcaster or blog about music, poetry readings, voice overs, or other audio, you need an audio plugin that’s clean, stylish, and easy to use. Compatibility is often a huge problem when working in this format as well. The WPaudio MP3 Player plugin takes care of a lot of that.

Like the video plugin, this one is pretty quick to set up and doesn’t seem to slow page loads down like many of the others available out there. I think the best features of this one are the controls themselves and its use of tags. It also works with HTML 5.

Smooth Slider

Neat features are not something WordPress is known for on its own. Even getting a basic set of columns and tables can be almost impossible, and often break more things than you have the patience to fix. The Smooth Slider Widget, however, seems to solve the problem.

Simple, fully customizable, and easy to use, you don’t have to know how to code to use it. It supports custom post types, pages, and media, pure images or image/text combinations. You can use your own text and even replace the number system. Definitely worth a try if you’re looking to add special features or update your site’s style.

Apture

Apture is all about search, and I have to admit, they do it well. Once installed:

Links are given a popout to their respective pages

Media is a snap to upload and imbed

Search for terms

You’ll find it’s easier for you to serve up the added content, without having visitors leave your site. They’ll be able to explore all they like, and can even search farther within the Apture window. I had this on my own blog for quite some time and really enjoyed it.

Lightbox Plus

If you use images to help explain a point, or like to feature images, but find you need a thumbnail and the ability to call up a larger image for a closer look, this is your plugin. It’s light, simple, and basic.

Fancy Box

An alternative is Fancybox. Similar in concept, this one is fully customizable, allows you to customize the various features, and is applied automatically. you can download it from WordPress.org and see it in action on Moskis. I’ve tried numerous ones (am currently testing another), and liked this one the best so far. Others easily became too complicated or lacked the basic functionality.

Incorporating Social Media

There are a ton of plugins available for the various sites, many of them work on a post by post basis and communicate back to the network. Unfortunately, there are just too many varieties to cover. My suggestion is to make a list of the features you want, have a look around, and try a few out.

Twitter Goodies

Available from WordPress.org, Twitter Goodies gives you a tweet button, search widget, and a profile widget. Quick, simple & clean

Simple Facebook Connect

No matter what you want to do with Facebook connect, this easy set of plugins will help you do it. There’s no need to be a coding wiz, either. Great for DIY-ers. You’ll find it on WordPress.org

Embed Facebook

Why waste your time posting the same thing twice, when you can post it on Facebook and embed it anywhere on your site you’d like? That’s what the Embed Facebook plugin does.

Social Bookmarking RELOADED

Why restrict your readers to only one or two social networks when you can let them share and save on whichever site they’d like? This one is neat and pretty comprehensive. Offered on WordPress.org.

Niche Specific Plugins

If you’re in a particular niche, why not use that to your advantage and offer something a little bit different that your visitors could actually use? Here are a few interesting ones:

Real Estate Finder

WP Flash Clock

If you give away hourly deals or otherwise use time in your marketing or niche, this could be an interesting one for you. You might even want to incorporate it right into your theme. You can find it here.

Protein Shake Recipe Calculator

Making protein shakes is a big thing for dieters and fitness nuts. Make it easy for them to figure out how many calories they’re consuming so they can stay on top of things. Available in a widget.

Foursquare Latest Checkins

I realize this probably should have gone in the social section, but to be honest, I thought this would be so great for a personal travel website, local review site, or even for marketing (traveling mascot), I had to move it to this section. Displays the latest checkins for a user. Get it on WordPress.org.

Have you used any rich media plugins? Which ones did you like the best?